1. Field of the Invention
The present invention relates to a unitary laser diode with an improved metal layer configuration, and more particularly, a submount integrated photodiode and laser diode package using the same which provides a light receiving area corresponding to a radiation area of light emitted from a laser diode, electrodes adjacent to the light receiving area and a metal layer functioning to radiate heat so as to reduce chip size in respect to a conventional one while maintaining a monitoring current identical with the conventional one as well as improve heat-radiating features.
2. Description of the Related Art
As well known in the art, a laser diode package emitting light via a laser diode is used in an optical pickup system, in which a photodiode used in the laser diode package detects the reflected quantity of emission light to adjust the output power of the laser diode. That is, the laser diode radiates backward about 10 to 30% of the total quantity of light emitted from a laser, and the photodiode detects and converts an optical signal radiated like this into a monitoring current Im. At this time, the laser diode can be sensed to continuously output a constant rated power through the monitoring current from the photodiode.
The laser diode generates heat while it emits light, in which the output power of the laser diode is lowered as the temperature is raised. As the power of the laser diode is lowered owing to high temperature, it is needed to apply higher input power to the laser diode in order to maintain the same output power. This consequently generates more heat thereby functioning as the most prominent reason which degrades the reliability of the laser diode or causes defects to the same. Therefore, it is important to consider heat-radiation in designing the laser diode.
In general, the photodiode in use for the laser diode is divided into a separate photodiode 110 as shown in FIG. 1A and a unitary photodiode 120 as shown in FIG. 1B. The separate photodiode is separated from a submount for mounting the laser diode, and is discriminated from the unitary photodiode in which the photodiode is integrally mounted to the submount and the laser mount is mounted on the photodiode. Using the unitary photodiode can advantageously reduce material cost and simplify assembly process, but disadvantageously deteriorate heat-radiating features thereby raising the temperature of the laser diode on the other hand. However, application of the unitary photodiode tends to gradually increase since it can reduce the cost of manufacture as well as advantageously implement downsizing. This accordingly increases the necessity for the optimized heat-radiating design.
FIG. 2 illustrates a conventional heat-radiating design of the unitary photodiode as set forth above.
As shown in FIG. 2, an Al layer (or metal layer) 230 is formed underlying a laser diode 210, and a light receiving area 220 is formed adjacent to the Al layer 230. The light receiving area is simply designed as a square without consideration of radiation features of the laser diode. Such a heat radiating structure, however, is designed without consideration of an unnecessary portion in the light receiving area which does not affect to the monitoring current Im.
It is therefore required to provide a laser diode package in which a light receiving area is formed based upon the heat-radiating features of the laser diode and a metal layer is accordingly designed so as to obtain the optimum heat-radiating performance.
The present invention has been made to solve the above problems and it is an object of the present invention to provide a laser diode package in which the configuration of a light receiving area and metal layer is optimally designed in an upper plane of a photodiode based upon a radiation area of a laser so as to reduce the size and improve heat-radiating features over a conventional art design while ensuring a monitoring current identical with that of the conventional one.
According to an aspect of the invention to obtain the above objects, the invention provides a submount integrated photodiode mounted with a laser diode and laser diode package using the same which comprises: a semiconductor substrate having lower electrodes at the bottom; a light receiving area provided in an upper plane of the semiconductor substrate, and configured identical with an area in the upper plane of the semiconductor substrate made by light emitted from the laser diode to receive the light emitted from the laser diode; a metal layer provided adjacent to the light receiving area to cover the upper plane except for the light receiving area; and a bonding layer positioned overlying the metal layer on the semiconductor substrate for mounting the laser diode.
In the submount integrated photodiode and laser diode package using the same of the invention, the light receiving area preferably has a substantially triangular configuration widening as extending from a position adjacent to the laser diode toward the end of the semiconductor substrate.